Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 5, 1999
Publication Date: N/A
Interpretive Summary: The success of integrated weed management relies on matching control strategies to the specific weed problem in a field. This requires information not only on what weed species and how many of these weeds are present in a field, but also knowledge of the distribution of the weeds throughout the field and the stage of development of these weeds. Weed control recommendations typically provide only information on appropriate tillage methods and herbicide selection with little consideration of the specific characteristics of the weed infestations. The objective of our research was to improve our understanding of the emergence characteristics of four important weed species, common waterhemp, giant foxtail, woolly cupgrass, and velvetleaf. The emergence patterns of the four species were distinctively different from each other. Common waterhemp began emerging later than the other species and had the longest period of emergence. Woolly cupgrass emergence began early and a high percentage of total emergence occurred soon after initial emergence. Although differences in emergence characteristics occurred among years of the study, each species displayed distinct emergence characteristics that were consistent. These characteristics are valuable to crop consultants and farmers as they evaluate weed problems and plan weed control programs. In addition, the consistency of emergence under varying conditions supports the potential to develop tools to predict weed emergence over broad geographic areas. These tools would improve weed control and reduce herbicide use by improving the timing and efficiency of field operations such as scouting, tillage, and herbicide application.
Emergence characteristics, including initial time of emergence, magnitude of emergence, and mean time of emergence, of common waterhemp, giant foxtail, woolly cupgrass, and velvetleaf were studied in central Iowa during the first three years following burial of seeds collected and buried in the fall of 1994 or 1995. Although the initial emergence date varied among years, the emergence sequence among species was consistent. Woolly cupgrass and velvetleaf were the first species to emerge with initial emergence occurring between April 28 and May 10. Initial emergence dates for these species were the same except for 1995 when velvetleaf emerged four days prior to woolly cupgrass. Common waterhemp was the last species to emerge, with initial emergence ranging from 5 to 25 days after velvetleaf. First year emergence in 1995 was 8% for velvetleaf, 7% for common waterhemp, 41% for woolly cupgrass, and 33% for giant foxtail. Emergence during the first year following burial in 1996 was similar to 1995 for velvetleaf and giant foxtail, but greater emergence was observed in 1996 for woolly cupgrass and common waterhemp. During the three years of the studies, cumulative emergence of the two grass species (43 to 71%) was higher than the broadleaf species (13 to 35%). A higher percentage of the total annual emergence occurred within the first two weeks after initial emergence of woolly cupgrass than the other species. Common waterhemp had the longest mean time of emergence due to extended periods of emergence throughout the growing season.